1. Field of the Invention
The present invention relates to a method of manufacturing a semiconductor device using semiconductor with crystallinity.
2. Description of the Related Art
There has been known a thin film transistor (hereinafter referred to as "TFT") using thin film semiconductor. The TFT is made up of thin film semiconductor formed on a substrate. The TFT is used in a variety of integrated circuits, and in particular, attention is paid to the TFT as a switching device disposed in each pixel and a driver device formed on a peripheral circuit section in an active matrix-type liquid-crystal display device.
Up to now, an amorphous silicon film has been employed as a thin film semiconductor for use in a TFT, but in order to obtain higher performance, an attempt has been made to use a silicon film (crystalline silicon film) having crystallinity.
The TFT using the crystalline silicon film enables higher speed operation than that using the amorphous silicon film by two digits or more, and enables the manufacturing peripheral drive circuit of the liquid crystal display device which has been formed of an external IC, on a substrate on which an active matrix circuit is also formed.
The conventional crystalline silicon film is obtained by crystallizing an amorphous silicon film formed through a plasma CVD method or a low pressure CVD method, by a heat treatment or the irradiation of a laser light.
However, the method of crystallizing the amorphous silicon film by heating suffers from the following problems although it has an advantage that the crystalline silicon thin film can be obtained over a large area.
(1) A high heating temperature is required (it is difficult to use a glass substrate). PA1 (2) The obtainable crystallinity is insufficient. PA1 removing a part of an amorphous silicon film formed on a substrate having an insulating surface to form a region for introducing metal elements that promote crystallization of silicon; PA1 allowing the region for adding said metal elements to selectively hold said metal elements; and PA1 conducting a heat treatment to allow crystal growth from said metal element added region toward a direction in parallel to the substrate. PA1 selectively controlling hydrophobic property of the surface of the amorphous silicon film to positionally control an introduced amount of said metal elements.
On the other hand, the method of crystallizing the amorphous silicon film by the irradiation of a laser light suffers from a problem that high productivity and large-area processing are difficult although it has superiority that a glass substrate can be used as the substrate.
Under the above-described circumstances, the present inventors have developed a technique in which metal elements that promote the crystallization such as nickel, palladium, lead or the like are added to the amorphous silicon film to obtain the crystalline silicon film through a heat treatment conducted at a lower temperature than the conventional one (refer to Japanese Patent Unexamined Publication No. Hei 7-130652).
This method not only enables a crystallizing rate to increase so that crystallization can be achieved in a short time, but also enables high crystallinity to be uniformly obtained over a large area in comparison with the conventional method of crystallizing the amorphous silicon film by only heating or the crystallization of the amorphous silicon film by means of only the irradiation of a laser light.
The above-described crystallizing method using the metal elements will be roughly described hereinafter. First, as shown in FIG. 5A, a silicon oxide film 502 is formed on a glass substrate 501 as an under film, and an amorphous silicon film 503 is then formed on the silicon oxide film 502.
Subsequently, UV rays are applied to the amorphous silicon film 503 in an oxygen atmosphere to form an extremely thin oxide film on a surface of the amorphous silicon film. This is for preventing a solution containing nickel which will be introduced therein later from being repelled by the surface of the amorphous silicon film.
Thereafter, a mask 504 made of the silicon oxide film is formed. Then, an opening 505 is then defined in the mask 504. Further, a solution containing nickel therein is coated on the surface, and a excessive solution is blown off by a spin coater, to thereby obtain a state where a small amount of solution is held as indicated by reference numeral 506 (FIG. 5B).
Sequentially, a heat treatment is conducted to make crystal growth in parallel with a substrate indicated by reference numeral 508.
In this process, the growth is hindered by the mask 504 made of the silicon oxide film.
It is presumed that this is caused by a stress exerted between the mask 504 and the silicon film, but its details are not clear.
In order to prevent this problem, it is proposed that after the state shown in FIG. 5B, the mask 504 is removed to conduct a heat treatment. However, in this case, nickel is also removed together, which will adversely affect crystallization to be conducted later.